Some who use cannabis for health reasons say it's transformative

"Within a month I was doing activities like walking up mountains and socialising in ways that I couldn't when I was bed ridden."

Image caption Greg de Hoedt is president of the United Kingdom Cannabis Social Clubs

Dr Zameel Caderof from Oxford University is running a major study on cannabis for medical use.

He says de Hoedt's experience is "far from the evidence that we need" but it "does support that we should be researching that area further".

Dr Caderof's research focuses on cannabinoids. These are found naturally in cannabis plants and the human body.

His study is looking at whether these compounds can help treat diseases.

"The plant contains very many different types of compounds, each with very unique properties and what we need to do is understand what each of these might be doing."

Cannabis is a class B drug and carries a maximum prison sentence of five years for possession and up to 14 years for supply and production. You can also receive an unlimited fine for possession, supply or production.